#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main() {
	float sum = 0;
	short f = 1;
	for (float i = 1.0; i <= 100; i++) {
		if (f) {
			sum += 1 / i;
			f = 0;
			continue;
		}
		sum -= 1 / i;
		f = 1;
	}
	printf("%f", sum);
	return 0;
}